Hydraulic brake booster pressure limiter

Abstract

The present invention is a pressure limiter for a hydraulic booster. The pressure limiter adjusts and limits the pressure generated between a pumping means and a restricting gap in a gain valve by limiting the size of the gap in response to sensed system pressure. A pressure limiter piston responds to system pressure to act against a gain valve piston and control the size of the gain valve gap.

What is claimed is: 
     
       1. A pressure limiter for a hydraulic booster, comprising: (a) a housing having, (I) a front end in opposed relation to a closed back end, (II) a first chamber adjacent the front end and extending longitudinally of the housing therefrom towards the closed back end, the first chamber having a fluid inlet through which fluid enters the first chamber, (III) a second chamber communicating with the first chamber in coaxial alignment and extending therefrom in the direction of the closed back end of the housing and having a greater cross-sectional area than that of the first chamber, the second chamber having a fluid outlet through which fluid exits the second chamber, and (IV) a gain valve bore communicating with the second chamber in coaxial alignment and extending therefrom in the direction of the closed back end of the housing;   (b) a gain valve piston slideably mounted in the gain valve bore and extending into the second chamber and being reciprocable in the bore and second chamber, the piston capable of sealing the first chamber from the second chamber to block the flow of fluid between the fluid inlet and the fluid outlet, as the piston approaches and abuts the first chamber;   (c) a second fluid inlet in the housing in communication with the gain valve bore and through which fluid, under pressure, enters the housing and engages and moves the gain valve piston towards the front end of the housing to seal the first chamber from the second chamber;   (d) means for biassing the gain valve piston in the direction of the first chamber; and   (e) means, operable by fluid under pressure, for engaging the gain valve piston and preventing the gain valve piston from abuting and sealing the first chamber to block the flow of fluid between the fluid inlet and outlet, said gain valve piston engaging means including, (I) a separate pressure limiter piston reciprocable in a bore that is separate from the bore of the gain valve piston from sealing the first chamber from the second chamber, and (II) means for biassing the pressure limiter piston in the direction of the front end of the housing.   
     
     
       2. The pressure limiter, as recited in claim 1, wherein the gain valve piston has a front end closer the front end of the housing and a back end closer the closed back end of the housing, and wherein the bore of the pressure limiter piston is disposed in the back end of the gain valve piston and extends longitudinally of said piston from the back and thereof towards the front and thereof, and wherein the closed back end of the housing has an opening extending longitudinally therethrough, and wherein the means for engaging the gain valve piston and preventing the movement thereof toward the first chamber includes: (I) a piston rod extending coaxially from the pressure limiter piston through the opening in the closed back end of the housing;   (II) means coacting between the piston rod and closed back end for sealing the space between the rod and walls of the housing defining the opening; and   (III) stop means coacting with the rod to stop movement of the pressure limiter piston towards the first chamber; and   (IV) an interlock means extending into the bore of the pressure limiter piston adjacent the back end of the gain valve piston to restrict said bore and maintain the pressure limiter piston in said bore; and which pressure limiter includes a booster side inlet passageway disposed in the housing between the back end of the piston and the closed end of the housing.     
     
     
       3. The pressure limiter as recited in claim 2 further comprising a back end chamber between the back end of the piston and the closed end of the housing, the booster side inlet passing through the housing into the back end chamber. 
     
     
       4. The pressure limiter as recited in claim 3 wherein the biassing means for biassing the pressure limiter piston includes a spring around the piston rod between the closed end of the housing and the pressure limiter piston. 
     
     
       5. The pressure limiter as recited in claim 4 wherein the end of the piston rod extends through the housing and the stop means is a piston retaining ring connected near the opposite end of the piston rod, the retaining ring having a greater diameter than the opening in the closed end of the housing whereby the piston rod is stopped from moving toward the first chamber by the intersection of the retaining ring and the outside wall around the opening in the closed end of the housing. 
     
     
       6. The pressure limiter as recited in claim 4 wherein the interlock means is a retaining ring connected to the inside wall of the gain valve piston bore and near the open end of the gain valve piston bore, whereby the piston intercepts the retaining ring when there is relative movement of the pressure limiter piston and the open end of the pressure limiter piston bore toward each other. 
     
     
       7. The pressure limiter as recited in claim 6 wherein there is a distance Y between the facing edges of the pressure limiter piston and retaining ring when there is a minimum pressure in the back end chamber. 
     
     
       8. The pressure limiter as recited in claim 6 wherein the pressure limiter piston and the piston retaining ring intercept when there is sufficient pressure in the back end chamber to slide the gain valve piston toward the front end of the housing and the pressure limiter piston toward the open end of the pressure limiter bore, there being a gap between the first chamber, the second chamber and the front end of the gain valve piston whereby the fluid pressure of fluid flowing from front inlet passage, through the gap to the outlet passage does not exceed a predetermined value. 
     
     
       9. A pressure limiter as recited in claim 4 further comprising a stem axially connected to the front end of the gain valve piston, the stem slidingly passing through a stem hole in the front end of the housing. 
     
     
       10. The pressure limiter, as recited in claim 1, wherein the bore of the pressure limiter piston includes a pressure limiter chamber which is disposed within the housing between the first chamber and front end of the housing and which is coaxially aligned with the first chamber and separated therefrom by a wall having an opening extending therethrough, the pressure limiter piston having a front portion and a back portion; and which pressure limiter includes: (I) a stem extending from the gain valve piston through the first chamber and opening in a wall into the pressure limiter chamber for contact with the pressure limiter piston when the pressure limiter piston moves a certain distance towards the first chamber; and   (II) means coacting with the pressure limiter piston for stopping movement of said piston toward the front end of the housing.     
     
     
       11. The pressure limiter as recited in claim 10 wherein the front portion of the pressure limiter piston is located to slide within the bore through the front end, further comprising a means to stop the front portion of the pressure limiter piston from sliding into the bore. 
     
     
       12. The pressure limiter as recited in claim 11 wherein the means to stop is an extension from the pressure limiter piston sidewall between the front portion and the back portion. 
     
     
       13. The pressure limiter as recited in claim 12 wherein the biasing means is a spring between the extension and the first chamber wall. 
     
     
       14. A pressure limiter for a hydraulic booster comprising: (a) a housing having at least three coaxially aligned chambers, the second chamber between the first and third chambers having a larger diameter than the other two chambers, the first chamber having a fluid inlet passageway and the second chamber having a fluid outlet passageway;   (b) a gain valve reciprocable in the third chamber and extending into the second chamber and forming with the second chamber an annular opening through which fluid passes between the fluid passageway, the annular opening becomming smaller as the valve moves toward the first chamber and being capable of being closed when the valve abuts the first chamber;   (c) a fluid inlet in the housing and communicating with the third chamber and through which fluid, under pressure, enters the housing and engages and moves the gain valve towards the first chamber to close the annular opening; and   (d) means operable by fluid, under pressure, for engaging the valve and preventing the movement thereof towards the first chamber beyond a position where the valve is in spaced relation from the first chamber to prevent closure of the annular opening.   
     
     
       15. The pressure limiter of claim 14, wherein the gain valve has a pair of opposing ends, and the means includes: (d) a fourth chamber in the end of the valve farthest from the first chamber;   (e) a piston reciprocable in the fourth chamber;   (f) means for maintaining the piston within the fourth chamber; and   (g) means for biasing the piston in the direction of the first chamber.   
     
     
       16. The pressure limiter of claim 15, which includes means for biasing the gain valve in the direction of the first chamber independently of the piston. 
     
     
       17. The pressure limiter of claim 16, which includes a fifth cylindrical chamber which is coaxially aligned and communicates with the fourth chamber, the fifth chamber being farthest spaced from the first chamber and including a fluid inlet passageway through which fluid enters the fourth and fifth chambers, the area of the piston closest the first chamber being greater than the area of the piston closest the fifth chamber, such that fluid, under pressure, within the fourth chamber acts to move the piston in a direction away from the first chamber. 
     
     
       18. The pressure limiter of claim 17, wherein the means for maintaining the piston in the fourth chamber includes an annular ring projecting into the fourth chamber adjacent the fifth chamber. 
     
     
       19. The pressure limiter of claim 14, wherein the means includes: (d) a fourth chamber coaxially aligned with the first chamber and spaced therefrom and out of communication therewith, the fourth chamber being farther spaced from the second chamber than the first chamber, the fourth chamber including an inlet through which fluid, under pressure, passes into the fourth chamber;   (e) a piston disposed in the fourth chamber and reciprocable along the longitudinal axis thereof;   (f) means for biasing the piston in a direction away from the first chamber; and   (g) means carried by the valve and extending into the fourth chamber for engaging the piston when the piston moves a predetermined distance in the fourth chamber towards the valve, to maintain the valve in predetermined spaced relation from the first chamber.   
     
     
       20. The pressure limiter of claim 19, which includes means for biasing the valve in the direction of the first chamber. 
     
     
       21. The pressure limiter of claim 20, wherein the means carried by the valve for contacting the piston includes, a rod coaxially affixed to the valve and extending therefrom through the first chamber into the fourth chamber.